The present invention provides a mechanical pipe-end expander comprising a cone and a die having tapered wedge bodies whose outer radius is larger towards a flangeless end direction from a flange end, wherein a pipe-end zone is expanded by a wedge effect of the die, which results from a procedure that the cone and the die are inserted together into the pipe-end zone to be expanded, and that then only the cone is axially drawn outwards leaving the die within the pipe-end zone. A seamless steel pipe with an expanded pipe-end zone is manufactured by applying a mechanical pipe-end expander comprising a die having tapered wedge bodies whose outer radius is larger towards a flangeless end direction from a flange end. The resulting seamless steel pipe has satisfactory pipe-end dimensional accuracy, and exhibits characteristics with excellent field welding workability.